Prior U.S. Pat. No. 4,365,926 discloses broadly a forklift assembly attached to an extensible and retractable boom. U.S. Pat. Nos. 3,001,654 and 3,288,316 disclose self-leveling forklift assemblies. U.S. Pat. No. 3,288,316 additionally discloses a master cylinder which responds to luffing of the boom to operate a slave cylinder connected between the boom and the forklift assembly to control the angular position of the latter.
The present invention has for its main objective to improve on the known prior art in a major way by providing a forklift variable reach mechanism for boom-type vehicles in which a self-leveling low profile twist-resistant forklift assembly and carriage is connected with the boom of the machine through a low profile parallelogram linkage, whereby the vertical height of the entire mechanism, when extended longitudinally of the boom, is approximately no greater than the depth or height of the boom base section.
A further object and feature of the invention is to provide a self-leveling low profile essentially self-contained forklift carriage unit which can be moved by a power cylinder of the low profile parallelogram linkage through a wide rotational range on the boom of the machine between elevated horizontal load-engaging positions and depressed positions including a position somewhat below ground level, when the boom is at a depressed angle below the horizontal. The mechanism can also assume a working position longitudinally coaxially with the boom to enable reaching into vertically confined spaces as small as eighteen inches in height.
Another important object of the invention resides in the provision of a variable reach forklift assembly in which the lifting forks are adjustably held on a very low profile twist-resistant carriage structure having a built-in torque tube and containing a pair of opposing power cylinders for adjusting the lifting forks or tines laterally, the two adjusting cylinders lying in a common plane close to the plane occupied by the forks and parallel thereto. The two cylinders are also in parallel relationship with the built-in torque or torsion tube, and lie substantially in a common plane therewith.
Other objects and advantages of the present invention will become apparent to those skilled in the art during the course of the following description .